German physicist August Toepler founded a photography technique that dates back to the mid-19th century. This technique known as the Schlieren Flow Visualization enables the photographer to visually capture the changes in air density.

This precious moment when air density is visible to the camera occurs in events like heat, turbulence and sound and in situations such as when pavements seemingly shimmer on a hot day from a distance, or how stars give the impression of twinkling. Basically the theory, explained in its most simple form is when light passes between these areas of different air density, it bends, distorting the viewers vision and creating a rather excellent photograph opportunity.

Scientists and engineers have begun to use this technique to see things that aren’t normally visible to the naked eye, like the the plume of a sneeze or the turbulence created around an airplane wing. The technique also has the ability to reveal what sound looks like, since it is also just a change in air density in the form of vibrations.